@kaeldy they are not descendants of any of the original breath of sun line. Tanjirou’s anscetor, Sumiyoshi learned it when he saved one of them. The memories of the Kagura dance have been passed down and perfected through Tanjirou’s ancestors, so Tanjirou knows how to use breath of the sun and see the invisible world because of his ancestors (who were not Breath of the Sun users, they were the users of the Kagura Dance) and their memories.
So the Kamados are badasses right from birth. Everytime that the murdered sliblings appears I try to imagine what'd be on a person who suffered that and keep on as Tanjirou. That's why he is one of the best MC around.
One anon mentioned reghtfully that we already seen 10 of the 12 moves of the dance.
@huyhuy14
his father and his grandfather were coal collectors, one of Tajirou's ancestors got the Hanafuda earrings. And thats and explanation that has yet to come.